In the past, FDMA (Frequency Division Multiple Access), OFDMA (Orthogonal Frequency Division Multiple Access), and other communication methods have employed methods for dividing the frequencies allocated to the entire system and allocating different frequencies to adjacent cells, in order to avoid interference with adjacent cells (see for example Patent Reference 1 below). FIG. 11 explains such a method of frequency allocation. In this method, as illustrated in the figure, for example different frequencies (A to C) are respectively allocated to three cells (cell #1 to cell #3). In particular, two terminal devices positioned in different cells near the cell boundary have different frequencies, so that there are few interference problems, and high-quality communication with the respective base stations is possible.
However, there are limits to allocable frequency resources. Hence when divided frequencies are allocated to individual cells, the bandwidth allocated per cell is narrowed relative to the entire frequency bandwidth. In the example of FIG. 11, this is “⅓”. Such an allocation method cannot allocate frequencies to each terminal device when numerous terminal devices exist within a cell, so that waiting for a free frequency occurs, and as a result the speed of transmission between terminal devices and base stations is degraded.
Hence in the prior art, methods have been used in which the frequency band per cell is broadened while avoiding interference with adjacent cells, to improve the speed of transmission in communication between base stations and terminal devices (see for example Patent Reference 2 below). FIG. 12A and FIG. 12B are used to explain such an example. For example, in a certain time period, frequencies allocated to a communication system as a whole are divided as illustrated in FIG. 12A, and different frequencies are allocated to adjacent cells. And, in a different time period, all frequencies of the communication system are allocated to each cell as illustrated in FIG. 12B. In this communication system, time periods are switched in alternation to perform communication.
Patent Reference 1: Japanese Patent Application Laid-open No. 2004-159345
Patent Reference 2: Japanese Patent Application No. 2007-999898